1. Field of the Invention
This invention pertains generally to a unique process and catalyst system for the production of a premium diesel from synthesis gas that is produced from natural gas, natural gas liquids, carbon dioxide, or other similar feedstocks. The present invention pertains to catalytic processes that allow for the elimination of costly and complex wax cracking, hydroisomerization, and/or other upgrading and refining steps, commonly employed in traditional Gas to Liquids (or GTL), thus enabling the economical production of diesel fuel or diesel fuel blending stocks from distributed production plants that typically produce less than 10,000 barrels per day, although much larger plants can use these processes.
2. Description of Related Art
Global demand for energy continues to rise at a significant rate, particularly among developing industrialized nations. Natural gas, natural gas liquids, waste CO2, associated stranded or flared gas, and combinations thereof are becoming more attractive as energy sources due to the increase in production of these gases worldwide.
It is known in the art that natural gas or other feedstocks outlined above can be converted into synthesis gas (or hydrogen and carbon monoxide) from a variety of known thermochemical conversion methods, including partial oxidation, auto-thermal reforming, steam methane reforming, dry reforming, and other practiced methods that are known in the art. Technologies for the production of syngas from other carbonaceous resources are also widely known and emerging processes are also under development.
The catalytic hydrogenation of carbon monoxide to produce light gases, liquids and waxes, ranging from methane to heavy hydrocarbons (C100 and higher) in addition to oxygenated hydrocarbons, is typically referred to Fischer-Tropsch (or F-T) synthesis. Traditional F-T processes primarily produce a high weight (or wt. %) F-T wax (C25 and higher) from the catalytic conversion process. These F-T waxes are then hydrocracked and/or further processed to produce diesel, naphtha, and other fractions. During this hydrocracking process, light hydrocarbons are also produced, which may require additional upgrading to produce viable products. Some of these processes are known and described in the art.
For example, U.S. Pat. No. 6,262,131 B1 (Syntroleum), issued Jul. 17, 2001, describes a structured Fischer-Tropsch catalyst system and method that includes at least one structure having a catalytic surface, such catalytic surface having a linear dimension exceeding 20 mm, a void ratio exceeding 0.6, and a contour that causes non-Taylor flow when CO and H2 pass through the structure. F-T catalysts, including iron and cobalt, are described in the patent.
U.S. Pat. No. 7,404,936 (Velocys, Inc.) issued Jul. 29, 2008, describes a micro-channel reactor system and catalysts used in the micro-channel reactor system to produce heavy hydrocarbons from a syngas steam.
U.S. Pat. No. 4,499,209 (Shell Oil Company), issued Feb. 12, 1985, describes a Fischer-Tropsch catalyst prepared by impregnation of a silica carrier with a solution of zirconium and titanium, followed by calcination and other preparation steps.
U.S. Pat. No. 5,620,670 (Rentech, Inc.), issued Apr. 15, 1997, describes a catalytic process converting hydrogen and carbon monoxide in a Fischer-Tropsch synthesis reactor using a promoted iron oxide catalyst slurry.
These patents describe catalysts that form high hydrocarbon reaction products (e.g., wax) that require further processing, including hydroprocessing and other upgrading processes, to produce diesel fuel or diesel blendstock (C8-C24).
Hydrocracking and other upgrading processes add significant expense and complexity to a plant design. Such processes can be justified for large, refinery scale plants such as traditional gas to liquids plants. However for smaller, distributed applications that require lower volumes of feedstock for gas-to-liquids (GTL), and other plants that produce less than approximately 10,000 barrels per day, plant designs that incorporate traditional F-T processes that include hydrocracking and other expensive upgrading processes may not be economically viable. To date, F-T type catalyst and catalytic process plant designs have not been available to support these smaller, distributed applications.
Accordingly, there is an increasing need for a catalytic process that can directly convert syngas into a diesel fuel with a high yield at relatively low cost under mild operating conditions. There is also a need for a catalytic process that does not require traditional major traditional hydrocracking and upgrading steps, thus enabling the economic production of distributed GTL. The present invention meets these needs as well as others and provides a substantial improvement over the prior art.